This invention relates to a method for preparing overbased molybdenum-alkaline earth metal sulfonates. More particularly, this invention relates to a process for producing overbased molybdenum-alkaline earth metal sulfonates wherein a highly effective friction-reducing and anti-rust-providing composition is produced. The products of the process of this invention are highly overbased molybdenum-alkaline earth metal sulfonates having a TBN (total base number) greater than about 300 (metal ratio greater than about 15), which products provide a combination of highly valuable properties to lubricating oils including friction modification, anti-oxidation properties, and anti-rust properties.
In U.S. Pat. No. 4,137,186, Sabol discloses a process for preparing overbased magnesium sulfonate dispersions by hydrating a magnesium-containing compound at an elevated temperature in the presence of an inert diluent, an alkanol, an oil-soluble sulfonic acid compound containing from about 1 wt% to 100 wt% oil-soluble ammonium sulfonate, a stoichiometric excess of a hydratable magnesium compound based upon the sulfonic acid compound, water, a lower alkanol, and at least one substantially inert diluent, heating the composition to hydrate the magnesium compound, after the hydration is completed, heating the mixture to remove substantially all of the lower alkanol, and then adding an acidic material to the mixture at a temperature within the range of about 26.7.degree. C. (80.degree. F.) to about 68.3.degree. C. (155.degree. F.) to form an amorphous magnesium suspension.
In U.S. Pat. No. 3,496,105, LeSuer teaches a process for preparing molybdenum-containing alkaline earth metal sulfonates wherein an overbased carbonated alkaline earth metal sulfonate is contacted with an inorganic composition including ammonium and alkaline earth metal salts of molybdenum-containing anion such as MoO.sub.4 and Mo.sub.7 O.sub.24. These products, which are prepared directly from overbased carbonate materials, suffer the disadvantage that the molybdenum incorporated in the composition can form a solid precipitate or a hazy precipitate, rendering the molybdenum-containing sulfonate material useless for lubricating oils. While haze in the lubricating oil composition does not always reduce the lubricant properties, solid precipitate can cause plugging of channels in engines and mechanical damage.
Accordingly, a need exists to provide a process for the preparation of molybdenum-alkaline earth metal sulfonate dispersions which provide anti-wear, anti-rust, and anti-oxidation properties to lubricating oils and which do not form molybdenum precipitate during storage.
There has now been found and developed an improved process for producing highly basic molybdenum-alkaline earth metal overbased sulfonates by an economical, efficient productive process resulting in substantial incorporation of the molybdenum into the sulfonate which, when added to a lubricating oil, provides substantial anti-rust, anti-oxidation, and anti-wear properties to the oil and reduces the coefficient of friction of the oil.